924Board.org

[gegge]

I am interested depending on design and specifications.

Looking for something more robust than Francos design. The Toyota VVT seems rigid but is hydralic. Guessing that a mechanical system with centrifugal weights is good enough shifting at 4000 rpm. The range in my opions should be +7/-3 degrees.
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[morghen]

[tyfighter123]

Im interested.

Tyler
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Porsche 924 1977 N/A
Mustang GT/CS 2007
Porsche 924S 1987 (parts car)(cut up and recycled)
Porsche 911S 1976
Porsche 931 1980
Porsche 931 1980 (parts car)

[gegge]

I was thinking yesterday and ended up with two suggestions of simple mechanic variable cam gears.

I am looking for simplicity and reability, hence few strong parts. I want a "limp-home" mode just in case of failure. Worst case is a cam gear that doesn´t work meaning locked in a position close to stock. A camgear that does work on an interference engine.

The coilspringload version work with the resulting torque when turning the cam. I belive that the torque required is proportional to the increased rpm. When not running or idle, the springs are at full lenght and the cam is advanced 10 degrees. The more you increase the revs, the more the springs get compressed. At a certain rpm they are fullt compressed and the inner impeller is touching the outer impelled of the cam gear. The gear has retarded the cam from 10 degrees advanced to stock.


The wedgeweight and spring version relies on the centrifugal force. At idle the springs are pressing the wedges to the center and advancing the cam fully. As the revs increase, the weight of the wedges are forced outwards and the gap between the impellers are decreasing and the cam is retarded to stock.

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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[MikeDanger]

heres the basic drawing, still a bit of work to do:


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It was either this or a giant box of legos

[Shurick]

[MikeDanger]

[!tom]

[morghen]

By no means i claim to be allknowing so dont get me wrong, i really am trying to help. I was also thinking of designing such a device but its very complicated and it would take me alot of time. I'm a design engineer, i have been designing parts and assemblies for the automotive industry for the past 7 years...so if you can take some constructive criticism..

Your design is weak and difficult to produce in a precise way.
Let me explain why and make a comparisson to the Franco gear which is also weak as it was proven to break and destroy engines.

Here is your weak point: The seating/sliding surface for the actuation is actually smaller than the Franco gear, the Franco gear uses an 6 or 8mm diameter pin on the drive plate that engages on the gear housing and controls the advance/retard curve.
So your mistake here is to design a smaller friction/seating/sliding surface than the Franco gear. The forces that are applied to this part and the amount of cycles this part will make are both very high. So you need to come up with a lot of surface for it to seat and slide on.
Also the tolerances and wear have to be taken into consideration in a safe way. If you have any play there you're in trouble...and you have to have some play to sync the two weights.

The next mistake is that the lever the weights make on the weak point is going to be pretty big, and the weak areas are small...so there is a chance that the metal will crack, bend or break in the weak area pointed out in the picture below.
Even if the profiles you designed to slide corectly with no torque applied i think the fatigue will break either the weights or the two teeth.




Think about the following statements when you design this:

1. Torque will be applied both clockwise and anti-clockwise on the part, it does not have to jam either way.
2. Sliding surfaces will wear, they have to be small enough to minimise friction but strong and big enough to take the loads applied to them.
3. Weights and their lever make the parts deform with vibrations.
4. Draw the parts in all their positions and judge what loads will they take in that position and think about cycles, and wear when dimensioning the features on the part.

You have to think it up from a dynamic perspective, take in consideration production, precision, vibration, loads, lifetime, assembly, dissasembly and more.
Good luck !
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Supercharger and EFI kits
https://www.the924.com

[gegge]

What about a modified planetry gear train?

The planetary gears are cut in half and the weight and centrifugal force rotate the gear some 90 degrees equivalent to 10 degrees on the internal gear.

Excuse the poor paintjob

_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[MikeDanger]

I will take your feed back of course, however I have taken into account the stresses and and not worried about failure in the places you have pointed out.
There are some other issues I will consider.
I may do something with some elemets from this one:


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It was either this or a giant box of legos

[Keefover]

Bump

Any progress? I'm interested in manufacturing these devices. Any help would be greatly appreciated. Seems to be some pretty great ideas being kicked around. I have a manufacturer that I work very closely with for other projects that is very excited about undertaking this project.

Jordan

[Fasteddie313]